MONTPELIER — Doctors and other health professionals would be immune from professional conduct charges if they pursued a hotly debated course of treatment for Lyme disease under a bill given preliminary approval Thursday by the Vermont Senate.

The Senate’s 27-0 vote in support came after an impassioned speech by Sen. David Zuckerman, a Chittenden County Progressive who said his wife, Rachel Nevitt, had suffered from the tick-borne illness for about a dozen years and had struggled to get medical professionals to recognize and diagnose the disease.

“My spouse had gone to her doctor for a number of years with cyclical ailments of achy joints, flu-like symptoms, except without fever, which is curious,” Zuckerman said.

Nevitt later went to a naturopathic physician, who ran a more expensive test than those ordered by her primary care provider. “When that test came back, it was quite clear from the markers on that test that she had Lyme,” Zuckerman said.

Before the diagnosis, Nevitt had developed neurological problems that made communication between the spouses difficult. “There were a couple of years when my marriage was about to dissolve,” Zuckerman said. The diagnosis of Lyme gave him an understanding that helped put the relationship back on a good footing, he said.

Vermont would join Connecticut, Massachusetts, Rhode Island and California as states that have protected doctors against professional conduct prosecutions if they prescribe long-term antibiotics — meaning for more than a month — to people with Lyme disease.

The treatment is widely considered experimental, with mainstream medical groups like the Infectious Diseases Society of America pointing to two types of side effects: One is in individual patients, who can develop debilitating diarrhea among other problems; the other is the general public, which loses the effectiveness of various antibiotics as bacteria evolve to be resistant.

Rep. George Till, D-Jericho and an obstetrician-gynecologist, said in an interview that a series of studies by the National Institutes of Health had “not demonstrated any long-term benefit from long-term antibiotics.”

Till said he ended up voting for the bill when it was in the House after working from his seat on the Health Care Committee to limits its scope. The bill’s language makes clear that doctors prescribing long-term antibiotics can be prosecuted if they are found at the same time to have violated professional standards in other ways.

“It isn’t a license to just go out and be a complete cowboy and try all sorts of crazy and experimental things,” Till said.